A new report says North Korea could have as many as 100 nuclear weapons by 2020. That includes the 16 to 20 such weapons the report's writer says the closed country already has. Not everyone agrees North Korea will be able to build that many more nuclear weapons in the next five years, but most experts believe it will have more nuclear weapons in 2020 than it has today.

The Institute for Science and International Security released the report this week. It said the number of nuclear weapons North Korea will have five years from now depends upon how fast the weapons are made. It also says North Korea is likely to be able to develop small nuclear weapons that can be placed on long-range missiles.

Not everyone agrees with the estimates, including South Korea's defense ministry. Kim Min-seok is a spokesman for the ministry. He says ministry officials do not think the North has as many nuclear weapons as the report suggests.

He says the analysis that North Korea has 10 to 16 nuclear weapons is just an assumption by some private groups and experts. He says there is no evidence to support this.

Bruce Bennett is a defense expert at the RAND Corporation, a research group. He does not believe North Korea can build enough nuclear weapons in the next five years to have 100 of them. He says making that many would require building and operating a new nuclear reactor and starting a strong program of uranium enrichment. He says the number is likely to be 50.

"If they have 50 nuclear weapons they can probably kill about, oh, 10 to 20 million people with those weapons. So that's a huge difference and it gives them significantly more coercive power against South Korea, against Japan and against the United States."

Experts say countries are not more dangerous just because they have more nuclear weapons. They say nations that have nuclear weapons do not use them because they know if they do, they will be attacked by other countries with such weapons. Experts call this "mutually assured destruction."

Daniel Pinkston is an expert on Korea at the International Crisis Group, which describes itself as an "independent, non-profit, non-governmental organization." Mr. Pinkston says because of the behavior North Korea's leaders have shown in the past, he is worried they might launch a nuclear attack.

"North Korea, because of how domestic politics work inside the country and how they use force and coercion to achieve their political aims, that they may attempt to use their nuclear arsenal to achieve their goals and objectives."

Bruce Bennett says it is possible North Korea might use nuclear weapons in an attack on other Asian nations because of political problems in the North. He also says the North might sell nuclear weapons to other countries or terrorists to use in an attack against the United States.

"It could try to sell them to third parties -- they could be nation-states that it tries to ally with. They could be terrorist groups. And if they're terrorist groups (it is) very hard to deter a terrorist group, and a terrorist group by and large would want to target the United States."

Shin In-kyun is an expert at the Korea Defense Network. He says the United States and its allies should attack North Korean missile centers before the North can develop nuclear weapons that can be placed on missiles.

He says now is the time to attack the missile sites with air strikes because North Korea does not now have the ability to attack the United States with nuclear weapons.

Other experts say such an attack could start a larger conflict.

Mr. Bennett says South Korea is building a system that would use ballistic missiles, cruise missiles, aircraft and armed unmanned planes called drones to attack North Korea if it launches a missile attack. The United States decided not to deploy a missile defense system in South Korea after China and the South voiced concerns.

Leaders of the United States and its allies do not believe they should recognize or negotiate with North Korea as a nuclear state. Experts say these leaders would lose political support if they did so. Even China and Russia, which support North Korea, believe the Korean peninsula should be free of nuclear weapons.

Negotiators involved in meetings include the United States, North and South Korea, China, Russia and Japan. So far those talks have failed to persuade North Korea to end its nuclear weapons program. The negotiators have told the North they would give more aid to the economically-poor country if it stopped building nuclear weapons.

The United Nations approved economic restrictions on North Korea after the North carried out a nuclear weapons test in 2013. Those sanctions have not caused the North to change its behavior. However, Mr. Pinkston says nations should continue to pressure the North to end its nuclear weapons program.

"North Korean leaders are, are rational. They wish to survive. I think they can be deterred. They are deterred up until today. They were deterred yesterday. And so deterrence continues to work."

He says the North's economy is suffering because of the country's decision to continue its nuclear program. He says the country cannot live with such suffering forever.